Are there any animal lovers in this house?

We have a 7 yrs old german sheppard. He is scared to death of a hose. A spray can, anything that has a hissing noise. Anyways, he's got some kind of skin problem. I've took him to the vet. several times. They say it's fleas. We treat them, and give him fatty capsules in his food. We've changed his food. Everything, and he is still, scratching and loosing his hair on the back side. They say it is not mange. The skin is very dry and flaky looking. The flaky looking skin seems to be piling up. And the dog is miserable. Do you think he could have scabies, maybe some mites? I just don't know what it is, or how to treat it. I may just end up taking him to another vet. This vet is costing a small fortune, with no results. Any wisdom on this subject would be appreciated.